A piezoelectric diaphragm pump sucks working fluid from a suction-valve and discharges the working fluid from an exhaust-valve by increasing and decreasing an inner volume of a pump room due to deformation of a diaphragm of a piezoelectric element. The diaphragm has a pair of electrodes provided on upper and lower faces of a disc shaped piezoelectric member. When a voltage is applied between the electrodes, the piezoelectric member is deformed, so that the diaphragm of the diaphragm pump is deformed, and the working fluid is sucked or discharged. As for the use of the sucking and discharging of the working fluid by the diaphragm pump, feeding of a whit quantity of alcohol to a fuel cell or electrostatic spraying of water can be cited. In these purpose, it is desirable that not only the liquid level configuration (or a face location) of the liquid at a front end of a discharge nozzle but also the rate of flow of the discharged liquid are stable. A suction stroke and a discharge stroke, however, are operated alternately in a reciprocation motion pump such as diaphragm pump, so that a pulsating quantity of the discharged liquid generally becomes larger. On the other hand, in a pump using a passive valve, back stream occurs due to switching action of the valve. Such a back stream can be reduced by using an active valve, but it causes an increase of cost.
Japanese Laid-Open Patent Publication No. 63-275888 discloses a conventional apparatus for preventing occurrence of pulsation in liquid flowing in a pipe arrangement with using a diaphragm, plunger or gear pumps. Such a conventional apparatus is comprised of a flexible pipe or flexible hollow ball member, and an elastic member for restricting a cross-section area of an aperture the pipe or the hollow ball member. When the liquid is flown with a pressure, the elastic member is deformed to vary the cross-section area of the aperture the pipe or the hollow ball member corresponding to the pressure of the liquid, so that the variation of the pressure of the liquid can be absorbed. The response of the elastic member to the variation of the pressure, however, is slower, so that the variation of the inner volume of the flexible pipe or hollow ball member is slower. Consequently, such a conventional apparatus can respond to only relatively large pulsation but cannot respond to minute back stream.
In addition, Japanese Laid-Open Patent Publication No. 10-75856 discloses a conventional pump apparatus having a long flexible tube provided in a path from an air pump to a pressing pipe arrangement and having predetermined inner dimensions in natural state. When a pressure acts on the inside of the flexible tube, it is expanded by the pressure, so that the pulsation of the liquid flow can be reduced. Since the pump apparatus uses the flexible tube, it cannot be respond to the minute back stream.
Furthermore, Japanese Laid-Open Patent Publication No. 11-281437 discloses a conventional flowmeter which absorbs pulsation of liquid flow so as to measure a rate of flow precisely. The flowmeter, however, is not assumed the back stream, at all.